1. Field of the Invention
The present invention relates generally to the patterning of a thin film on a surface. More particularly, the present invention relates to a method of depositing by a solution-based technique a patterned thin film onto a surface that has been selectively patterened with a self-assembled molecular monolayer.
2. Description of the Prior Art
Solution-based thin film deposition processes, such as spin-coating and immersion-coating, i.e., dip-coating, provide simple, low-cost, low-temperature routes to thin film deposition on large-area solid substrates.
Spin-coating and dip-coating are long-tested techniques commonly used to deposit thin films of a wide variety of materials for a broad range of applications. These materials include, as examples, organic materials, such as small molecules, oligomers, polymers, and photoresists; organic-inorganic hybrid materials; soluble inorganic materials, such as salts; suspensions; dispersions, such as silica particles or nanocrystalline materials; and metallo-organic complexes. The metallo-organic complexes may be converted to inorganic materials upon decomposition during high temperature annealing, a process known as “metal organic deposition.”
The above thin film materials are metallic, semiconducting, insulating and superconducting. They are used in many optical, electrical, magnetic, and structural applications.
U.S. Pat. Nos. 4,916,115 and 4,952,556, both to Mantese et al., describe patterning techniques. Thus, U.S. Pat. No. 4,916,115 describes techniques used to pattern spin-coated metallo-organic thin films by locally pyrolyzing deposited molecules. U.S. Pat. No. 4,952,556 describes techniques used to pattern spin-coated metallo-organic thin films by locally decomposing spin-coated metallo-organic thin films to form patterned insoluble inorganic materials upon dissolving remaining metallo-organics in an organic solvent.
U.S. Pat. No. 5,512,131 to Kumar et al. describes a method of patterning a surface that employs microcontact printing, also known as “stamping,” to form patterned molecular monolayers on the surface of a substrate.
U.S. Pat. No. 5,620,850 to Bamdad et al. describes microcontact printing, which has been used to deposit self-assembled monolayers (SAM) that have tail groups to sense biological materials.
N. L. Abbott et al., Science, 257, 1380(1992) describes the use of self-assembled monolayers (SAM) that have tail groups to control the placement of liquids on surfaces.
U.S. Pat. No. 6,020,047 to Everhart et al. describes the use of self-assembled monolayers (SAM) that have tail groups as indicators of analytes.
U.S. Pat. No. 5,900,160 to Whitesides et al. describes the use of patterned monolayers as masks for etching thin films.
N. J. Jeon et al., J. Mater. Res., 10(12), 2996(1995) describes the use of microcontact printing to prepare patterned metal-oxide thin films deposited from sol-gel precursors.
M. Era et al., Appl. Phys. Lett., 65, 676(1994) describes organic-inorganic hybrid materials that form the emissive layers in light-emitting diodes.
K. E. Paul et al., Appl. Phys. Lett., 73, 2893(1998) describes exposure of patterned photoresist features to UV radiation.
The contents of all of the above patents and publications are incorporated herein by reference in their entirity.
For many applications, thin films must be patterned to provide control over the film's spatial geometry. Spin- and dip-coated thin films have been patterned by subtractive processes, such as photolithography, etching, e-beam, ion-beam, or laser beam techniques and their combinations.
Etching spin- or dip-coated thin films exposes the deposited material to potentially harsh etching solutions or environments and may degrade the desirable materials properties (e.g., electrical, optical, magnetic, or structural) of the thin film.
Etching also requires multiple processing steps making it both more complex and costly. For example, using photolithography to define etch pattern requires photoresist to be applied, exposed to radiation, and developed before etching the material. In a final step, the remaining photoresist may be removed.
Interaction between the thin film material and the resist, radiation, or solvents/developer used in the lithography process may also degrade the deposited thin film. Accordingly, e-beam, ion-beam, or laser beam techniques are another set of alternative routes to patterning thin films.
These focused beam techniques are serial “writing” processes that are slow and therefore inherently more costly when large areas of the film must be modified. In addition, E-beam and ion-beam techniques must be carried out in vacuum chambers.
These techniques have been used, for example, to pattern spin-coated metallo-organic thin films by locally pyrolyzing deposited molecules, as described in the previously incorporated U.S. Pat. No. 4,916,115, and by locally decomposing spin-coated metallo-organic thin films to form patterned insoluble inorganic materials upon dissolving remaining metallo-organics in an organic solvent, as described in the previously incorporated U.S. Pat. No. 4,952,556.
These applications of focused beams to pattern thin films can lead to redeposition of undesirable materials, in the case of pyrolysis, and to possible material degradation by solvents used to remove the remaining metallo-organics, in the case of local decomposition.
In general, lithographic and focused beam techniques all require the use of a relatively complicated and costly apparatus to prepare patterned thin films. Resists, solvents, and developer used in these processes are also consumed, thus producing undesirable waste.
Alternative routes have been explored to deposit patterned thin films by low cost solution processes. All of these alternative techniques, notably ink-jet printing, screen-printing, and micromolding described herein below, have only been tested for a limited number of materials systems, each giving rise to a variety of limitations.
Thus, ink-jet printing is a sequential deposition technique, making it slow and therefore, more costly. It also has limited resolution caused by the spreading of the printed solution over the solid substrate surface. Furthermore, it can be limited by the viscosity and flow properties of the printed solution.
In the screen-printing method, thin films are deposited by spreading a solution of material over a screen in contact with the solid substrate surface. As in ink-jet printing, screen-printing is typically limited to low resolution applications by the inability to define high resolution features in the screen mask and by restrictions on the viscosity and flow properties of the printed solution.
Micromolding in capillaries is a technique in which an interconnected system of recessed channels, formed by placing a topographically modulated elastomeric stamp in contact with a substrate surface, is filled by capillary action on a drop of fluid containing the pre-polymer into a channel at one edge of the stamp. The pre-polymer is cured and the stamp is removed from the substrate surface, leaving an interconnected system of microstructures.
Micromolding in capillaries is slow and can be advantageously used only with solvents that (1) have low viscosity and (2) do not swell the stamp elastomer. This approach is further limited to patterning relatively large, micron-size features over small patterned areas. The pattern is restricted by the channel structure to extend to the edges of the stamp and to form interconnected and not isolated microstructures.
Microtransfer molding is a related technique in which a fluid pre-polymer is filled in indentations of a topographically modulated elastomeric stamp, is transferred to the substrate by bringing the stamp and substrate into conformal contact, and is cured to form a solid, allowing the stamp to be removed. As above, microtransfer molding is limited to large feature sizes and to materials that do not swell the stamp. An additional problem with this technique is the formation of an undesirable thin layer of material in regions where the stamp and the substrate surface make contact.
Thus, a need exists in the art for a simple, low-cost, low-temperature route to patterning thin films that are deposited by the well-developed and broadly applied solution deposition techniques, such as spin- and dip-coating, which route does not require potentially damaging post-deposition processing of these thin film materials.